Manganese-activated, magnesium-zinc fluorogermanate phosphor



Sept. 9, 1958 L. THoRlNGToN 2,851,425

MNGNESE-ACTIVATED, MAGNESIUM-ZINC FLUOROGERMANATE PHOSPHOR Filed April2, 195e 5 o s 001.55 2nd FE@ MM5 0F Pfl/0512,90@ INVEN TOR.

NGNESEAC TWATED, MAGNESIUM-ZINC FLUUROGERMANATE PHOSPHOR ApplicationApril 2, 1956, Serial No. 575,486 2 Claims. (Cl. 252-30145) Thisinvention relates to phosphor materials and, more particularly, tophosphor materials which are useful in converting ultra violet radiationto red-rich visible radiation, and this application is acontinuation-in-part of application Ser.'No. 126,506, filed Nov. 10,1949, now Patent No. 2,748,303 issued May 29, 1956, titled Color-Corrected Light Source, Phosphors Therefor and Method by LukeThorington, the inventor herein, and assigned to the assignee of theinstant application.

Phosphor materials having a predominantly red radiation are few innumber. Such phosphor materials are useful in fluorescent lamps andsimilar applications in order to add red radiation to improve the colorrendition for the light source so that objects illuminated by the lightsource will display a healthful and natural appearance.

ln this aforementioned parent application, Ser. No. 126,506, there isdisclosed a phosphor material having the molecular formula is a numberlying in the range between and including 2 and 6, y is a number lying inthe range between and including 2 and 0.1, and z is a number lying inthe range between and including 0.001 and 0.1. This phosphor ischaracterized by the fact that when excited by ultra violet radiationsover a substantial rangel of exciting wave lengths, it emits substantialand effective quantities of radiation in the red region of the visiblespectrum when subjected to and maintained at elevated temperatures forprolonged periods of time. The preferred formulation for thismanganese-activated magnesium uorogermanate phosphor is3.5Mg0.5MgF2GeO2:0.0lMn.

It is the general object of this invention to provide an improvedphosphor material which has a high output in the red region of thespectrum.

it is a further object to provide a phosphor material which has improvedoutput in the shorter wave length visible radiations and an output peakwhich is shifted toward the deep red as compared to manganese-activatedmagnesium iluorogermanate phosphor.

The aforesaid objects of the invention, and other objects which willbecome apparent as the description proceeds, are achieved by adding tothe magnesium fluorogermanate phosphor from 0.1 mole to 1.5 moles ofzinc oxide.

For a better understanding of the invention reference should be had tothe accompanying drawing wherein Fig. l represents the spectraldistribution for the phosphors of this invention as compared to themagnesium fluorogermenate phosphor described in thev aforementionedparent application;

Pig. 2 represents relative luminescence brightness for the phosphors ofthis invention as compared to the phosphors described in Patent No.2,447,449 to Williams.

In U. S. Patent No. 2,447,448 to Williams is described a magnesiumgermanate phosphor activated by manganese, the preferred formulation forthis phosphor being 4MgO-Ge02cMn. In U. S. Patent No. 2,447,4-49 toWilliams there is described a phosphor wherein limited nite StatesPatent O preferred magnesium iluorogermanate phosphor,

amounts of zinc oxide are substituted for an equivalent amount ofmagnesium oxide in the magnesium germanate phosphor in order to increasethe elliciency of the magnesium germanate phosphor.

It has been found that a zinc oxide addition to the magnesiumfluorogermanate phosphor described in parent application Ser. No.126,506 will improve the response of the phosphor in the orange regionof the spectrum and in addition will shift the maximum output peakfurther toward the deep red. It has been found that the zinc additionsto the phosphor may be made from 0.1 mole to 1.5 moles with the rest ofthe phosphor constituents remaining as in the phosphor of the heretoforementioned parent application with the optimum formulation for theimproved phosphor of this invention being about3MgO-.SMgFznSZnO-GeOgLOlMn. Thus the new and improved phosphor materialof this invention has the molecular formulation wMgO -xMgF2 -yZnO Ge02zMn, Where w is from 2 to 6, x is from 0.1 to 2, y is from 0.1 to 1.5and z is from 0.001 to 0.1. Without these constituent limitations, theutility of the improved phosphor is limited.

In Fig. 1 is shown the effect on spectral distribution under 3650 A. U.excitation when varying the zinc oxide content with respect to themagnesium oxidecontent for the improved phosphors of this invention. Inorder to compare the phosphors of this invention with the phosphorsdescribed in the aforementioned Williams patents, the Zinc oxide hasbeen indicated as substituted for an equal molar amount of magnesiumoxide in the preferred formulation for the manganese-activated magnesiumfluorogermanate. At the maximum substitution of 1.5 moles ZnO, theformulation for the phosphor will `be 2MgO-.5MgF2-1.5ZnO-GeO2:Mn. Itshould be clear that whether the zinc oxide is expressed as asubstituent for the magnesium oxide in the magnesium uorogermanate or asan additive to the phosphor, the effects are the same provided theconstituents of the improved phosphor of this invention are maintainedwithin their aforementioned limitations. As observed in Fig, 1, whereinrelative luminescence intensity in arbitrary units is plotted vs.wavelength in millimicrons', for the preferred magnesium fluorogermanatephosphor having no zinc oxide substitutent or additive, there is apronounced dip in the spec tral curve at about 640 mu. Where from 0.5 tol mole of zinc oxide is substituted for an equivalent molar amount ofmagnesium oxide in the preferred magnesium tluorogermanate phosphorthere is much less dip at 640 mu and the output peak in the red isshifted slightly toward the deeper red. At 1.5 moles Zinc oxidesubstitution in the the dip at 640 mu is almost eliminated and there isa further shift in the output peak for the phosphor toward the longerwave lengths. It has been found that in order for the zinc oxideadditive or substituent to have any measurable effect on the spectraldistribution, there should be at least 0.1 mole of zinc oxide, and withmore than 1.5 moles of Zinc oxide per mole of the magnesiumfluorogermanate the phosphor output decreases considerably.

In the upper curve of Fig. 2 is plotted relative luminescence brightness(in arbitrary units) vs. moles of zinc oxide substitution for magnesiumoxide per mole of magnesium fluorogermanate phosphor; wherein the ZeroZnO substitution represents the preferred magnesium iluorogermanate. Inthe lower curve in Fig. 2 are indicated the luminescence brightnessreadings for the phosphors as described in the aforementioned Williamspatents, Nos. 2,447,448 and 2,447,449. In both curves of Fig. 2 theexciting radiation is 3650 A. U. The phosphor material 4MgO-GeO2zMn isindicated at the zero ZnO substitution for the lower curve, whichphosphor has an output of 50 units as compared tothe output of 100 unitsfor the preferred magnesium uorogermanate phosphor.

Phosphors formulated in accordance with the Williams Patent No.2,447,449 are indicated in the remaining portions of the lower curve inFig. 2 and as shown, increasing the amount of zinc additive, orsubstituent, as the terminologymay indicate, decreases the outputsomewhat. As noted before, the zinc oxide component for the-phosphormaterials has been treated as a substituent for the magnesium oxide,since this terminology was used by Williams, and for purposes ofcomparison with the prior art, the same terminology is used indescribing the curves of Figs. 1 and 2. However, it does not matterWhether one considers the zinc oxide an additive to the phosphormaterial or a substituent for the magnesium oxide component thereof, aslong as the phosphor constituents are maintained within the aforestatedlimitations.

Referring again to the upper kcurve shown in Fig. 2, as zinc is includedinthe phosphor, the brightness does not increase, but as noted in Fig.1, the spectral distribution for the phosphor does shift. The point atwhich maximum spectral shift is achieved without decreasing the relativeluminescence brightness for the phosphor is 0.5 mole ZnO and for thisreason this amount of zinc oxide is chosen as optimum. With more than0.5 mole of ZnO per mole of phosphor the relative luminescencebrightness for the phosphor decreases with respect to the magnesiumfluorogermanate per se, but as shown in Fig. 1 the spectral distributionfor the phosphor continues to shift. With more than 1.5 moles of ZnO,per mole of phosphor, the relative luminescence brightness for -thephosphor decreases considerably.

The following are specific examples for preparing the phosphor materialsof this invention.

MnCO3 The foregoing constituents are water in a mortar and pestle. Thesemixed and wetted constituents are dried at C.. and are remixed dry andred in platinum trays at a temperature of 1080" C. for 1 hour. The firedphosphor is ballmilled 1 hour and then retired at 1080 C. for from 4 to48 hours.

mixed wet with distilled Example 2 Constituents 2 M oles M gO 2.0 MgF20.5 ZnO 1.5 GeOZ 1.0 MnCO3 0.01

The milling and ring procedures as given for Example l may be used forpreparing the constituents for Example 2.

It will be recognized that the objects of the invention have beenachieved by providing a phosphor material having improved luminescencein the orange region of the spectrum at about 640 mu, which phosphoralso has an output peak which is shifted slightly toward the deep red.

While in accordance with the patent statutes, one best known embodimentof the invention has been illustrated and described in detail, it is tobe particularly understood that the invention is not limited thereto orthereby.

I claim:

1. A phosphor material having the molecular formulawMgO-xMgF2yZnOGeO2:zMn, in which w is from 2 to 6, x is from 0.1 to 2, yis from 0.1 to 1.5 and z is from 0.001 to 0.1.

2. A phosphor material having a molecular formula of about3MgO-0.5MgF2O.5ZnO-GeO2:0.01Mn.

References Cited in the le of this patent UNITED STATES PATENTS2,447,448 Williams Aug. 17, 1948 2,447,449 Williams Aug. 17, 19482,748,303 Thorington May 29, 1956

1. A PHOSPHOR MATERIAL HAVING THE MOLECULAR FORMULAWMGO.XMGF2.YZNO.GEO2:ZMN, IN WHICH W IS FROM 2 TO 6, X IS FROM 0.1 TO 2,Y IS FROM 0.1 TO 1.5 AND Z IS FROM 0.001 TO 0.1.